Prior art temperature compensated integrated circuits (IC) are used mostly in the battery management systems. U.S. Pat. No. 5,955,869 discloses a method for monitoring remaining capacity of a battery pack. There are two different procedures that are used to estimate the battery pack remaining capacity. In a first procedure, data is generated on the battery pack to estimate remaining battery capacity; and in the second procedure, data transmitted to the battery pack from a host device is used to estimate remaining battery capacity. The battery pack switches between these two procedures. For example, the battery pack switches from the first procedure to the second procedure when the battery current falls below a threshold value.
More specifically, the '869 patent discloses a smart battery device installed in a host computer that optimizes the performance of the rechargeable battery throughout its life cycle. The smart battery device includes ASIC further comprising the following five basic blocks: processor core (CPU), analog to digital converter (A/D), program memory and look-up tables (ROM), data memory (RAM), and the I2C/SM Bus communications interface. The primary goal of these components is to measure, calculate, and communicate the status of the smart battery. Each of the above blocks includes additional hardware and software components required to perform the specific task. Some of these components are shared between components, such as the internal clock oscillator which is used by the CPU and the A/D. The calibration technique used in the '869 patent requires two values, a slope adjustment, and a correction offset. The temperature measurement requires two values made by an on-chip temperature measuring device. A ROM memory stores software for the calibration program, and A/D converters are used to convert voltage measurement to digital signals.
U.S. Pat. No. 5,841,996 discloses a serial communication interface system having programmable micro controller for use in a battery pack. The micro controller includes a microprocessor and various front-end analog circuitry such as a slope A/D converter and a multiplexer for allowing a plurality of analog input signals to be converted to corresponding digital counts indicative of signal level. In order to make the measurements of the selected analog inputs more precise, the micro controller utilizes a calibration procedure of the band-gap reference circuit which eliminates the need for an external reference voltage source. In order to obtain an actual measurement of the voltage supplied by band-gap reference circuit, the output voltage of band-gap reference circuit is selected, and using precision voltage measurement circuitry, the band-gap voltage is accurately measured and stored in EPROM. The absolute magnitude of the output voltage of thermistor is also measured at a predetermined temperature and also stored in EPROM. The temperature coefficient of the thermistor is calibrated at two or more various temperatures to improve accuracy.
Thus, to achieve a really high absolute accuracy and a low temperature drift, a prior art temperature compensated IC circuit needs to be calibrated at two or more distinct temperatures after packaging. However, calibrating an integrated circuit (IC) at two or more temperatures is an expensive procedure in terms of test time, test equipment and test logistics.
What is needed is to reduce the test equipment logistics and test time required to calibrate a temperature compensated IC circuit in an efficient manner.